Washing machine and method for controlling the same

ABSTRACT

A washing machine and a method of controlling the same are disclosed. If two washing tubs simultaneously perform the dehydration, unbalanced positions of the first and second washing tubs are checked. The method controls dehydration rotation speed or dehydration rotation direction of each washing tub to adjust a difference in unbalanced position angle between two washing tubs, thereby reducing vibration. If dehydration is performed in one washing tub, the method prevents the other washing tub performing no dehydration process from entering the dehydration process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2009-0037412, filed on Apr. 29, 2009 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field

Embodiments of the present invention relate to a washing machine having a plurality of washing tubs to clean laundry in different ways based on capacity and types of clothing, and a method of controlling the same.

2. Description of the Related Art

Generally, a washing machine (for example, a drum washing machine) includes a single washing tub, and separates pollutants or contaminants from dirty laundry using water and detergent. The washing machine washes or cleans the dirty laundry using a series of processes, i.e., a washing process to separate a pollutant or contaminant from laundry with water containing a detergent, a rinsing process to rinse bubbles or residual detergent out of the laundry with clean water (specifically, rinsing water), and a dehydration process to dehydrate the laundry at high speed.

In recent times, a drying function has been added to the washing machine, so that the washing machine can perform a drying process to dry dehydrated laundry. However, because clothing generally has different kinds and different material qualities, the washing machine may have difficulty in simultaneously cleaning all the laundry contained in one washing tub using one washing course. The washing machine including one washing tub separates some clothing, which cannot be simultaneously cleaned, from other clothing capable of being simultaneously cleaned. Thus, the separated clothing requires additional washing. In this case, a user suffers substantial inconvenience when using the washing machine because a separate washing operation is needed for some clothing, and the user has to drive the washing machine several times (e.g., twice), so that time and energy may be excessively consumed. Although the user wants to wash or clean only a small amount of clothing, if a washing tub is a large-capacity washing tub, the small amount of clothing must be washed or cleaned in the large-capacity washing tub, resulting in unnecessary power consumption.

SUMMARY

Therefore, it is an aspect of the present invention to provide a method of reducing vibration of a washing machine by adjusting unbalanced positions of two washing tubs contained in the washing machine operating in a dehydration process.

It is another aspect of the present invention to provide a method of controlling a dehydration rotation direction and a dehydration-process entry or non-entry status during a dehydration process of the washing machine having two washing tubs, thereby reducing vibration of the washing machine.

Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.

The foregoing and/or other aspects of the present invention may be achieved by providing a method of controlling a washing machine having a first washing tub and a second washing tub, the method including determining whether a dehydration operation is performed in the first and second washing tubs; and reducing vibration of the washing machine comprising adjusting the dehydration operation of the first or second washing tub.

The determining whether the dehydration operation is performed in the first and second washing tubs may include: determining, when one of the first and second washing tubs is in a dehydration process, whether the other washing tub having no dehydration status reaches a dehydration process.

The method may further include: controlling, if the other washing tub having no dehydration status reaches the dehydration process, a dehydration operation of the other washing tub in such a manner that a dehydration rotation is performed in an opposite direction to another dehydration rotation of the one washing tub in which the dehydration process was performed earlier than that of the other washing tub.

The method may further include: controlling, if the other washing tub having no dehydration status reaches the dehydration process, a dehydration operation of the other washing tub to prevent the other washing tub from entering the dehydration process until the one washing tub performing the dehydration operation stops the dehydration operation.

The determining whether the dehydration process is performed in the first and second washing tubs may include: determining whether the first and second washing tubs simultaneously reach the dehydration process.

The method may further include: setting, if the first and second washing tubs simultaneously reach the dehydration process, different dehydration rotation directions to the first and second washing tubs, so that dehydration operations of the first and second washing tubs are performed in different directions.

The method may further include: adjusting, if the first and second washing tubs simultaneously reach the dehydration process, a dehydration operation of the washing tub in such a manner that the dehydration operation is performed only in one of the first and second washing tubs.

The method may further include: adjusting a dehydration operation of a washing tub having no dehydration status in such a manner that the washing tub performs the dehydration operation when the dehydration operation of the other washing tub is completed.

The determining whether the dehydration process is performed in the first and second washing tubs may include: determining whether the first and second washing tubs simultaneously perform the dehydration process.

The method may further include: checking an unbalanced position of each of the first and second washing tubs when the first and second washing tubs simultaneously perform the dehydration process.

A first drum may be rotatably installed in the first washing tub, and a second drum may be rotatably installed in the second washing tub. The unbalanced position may be checked by detecting a rotation speed of the first or second drum.

The checking of the unbalanced position by detecting the rotation speed of the first or second drum may include: checking a position at which rotational acceleration of the first or second drum becomes zero.

The checking of the unbalanced position by detecting the rotation speed of the first or second drum may include: determining that the unbalanced position exists in the highest point of the first or second drum at a time point at which the rotational acceleration becomes zero in response to the increasing and decreasing of the rotation speed of the first or second drum.

The checking of the unbalanced position by detecting the rotation speed of the first or second drum may include: determining that the unbalanced position exists in the lowest point of the first or second drum at a time point at which the rotation acceleration becomes zero in response to the increasing and decreasing of the rotation speed of the first or second drum.

The method may further include: adjusting, if the unbalanced position of the first or second washing tub is checked, an unbalanced position of the first or second washing tub, and reducing vibration of the washing machine.

The adjusting of the unbalanced position of the first or second washing tub may include: controlling a difference between a first position angle of an unbalance of the first washing tub and a second position angle of an unbalance of the second washing tub to be equal to or larger than a reference angle, thus adjusting the unbalanced position.

The adjusting of the unbalanced position of the first or second washing tub may include: adjusting the unbalanced position by adjusting a dehydration rotation speed of the first or second washing tub.

The method may further include: setting, if the dehydration process is simultaneously performed in the first and second washing tubs, different dehydration rotation directions to the first and second washing tubs, and adjusting dehydration operations of each of the washing tubs.

The method may further include: checking a dehydration rotation speed of the first and second washing tub; and changing a rotation direction of one washing tub having a relatively slow dehydration rotation speed from among the first and second washing tubs to another rotation direction, and adjusting the dehydration operation of the washing tub.

In accordance with another aspect of the present invention, a washing machine includes: a plurality of washing tubs; and a controller which checks whether a dehydration operation is performed in each of the washing tubs, adjusts the dehydration operation of each of the washing tubs when the dehydration operation is performed in each of the washing tubs, and reduces vibration of the washing machine.

The plurality of washing tubs may include a first washing tub in which a first drum is rotatably installed and a second washing tub in which a second drum is rotatably installed. The controller may reduce vibration of the washing machine by adjusting rotation operations of the first and second drums.

The washing machine may further include a speed detector to detect a speed of the first or second drum.

The controller may check an unbalanced position of the first or second washing tub according to a speed of the first or second drum.

The controller may reduce vibration of the washing machine by adjusting an unbalanced position of the first or second washing tub.

The controller may adjust a difference in an unbalanced position between the first washing tub and the second washing tub to be equal to or larger than a reference angle.

The controller may reduce vibration of the washing machine by controlling the first and second drums to have different dehydration rotation directions opposite to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a perspective view illustrating the appearance of a washing machine according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a washing machine according to the exemplary embodiment of the present invention.

FIG. 3 is a control block diagram illustrating a washing machine according to an exemplary embodiment of the present invention.

FIGS. 4A and 4B illustrate unbalanced positions caused by laundry contained in a washing machine according to an exemplary embodiment of the present invention.

FIG. 4C is a graph illustrating a variation of dehydration speed under an unbalanced status of a washing machine according to an exemplary embodiment of the present invention.

FIGS. 5A and 5B are conceptual diagrams illustrating positions of unbalance occurring in a dehydration rotation operation of a washing machine according to an exemplary embodiment of the present invention.

FIG. 6A is a flow chart illustrating a method of reducing vibration in a dehydration process of a washing machine according to an exemplary embodiment of the present invention.

FIG. 6B is a flow chart illustrating a method of reducing vibration in a dehydration process of a washing machine according to another exemplary embodiment of the present invention.

FIG. 6C is a flow chart illustrating a method of reducing vibration in a dehydration process of a washing machine according to another exemplary embodiment of the present invention.

FIG. 6D is a flow chart illustrating a method of reducing vibration in a dehydration process of a washing machine according to another exemplary embodiment of the present invention.

FIG. 7 is a flow chart illustrating a method for controlling an unbalanced position of a washing machine according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.

FIG. 1 is a perspective view illustrating the appearance of a washing machine according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the washing machine 100 includes a main body 301 forming an external appearance, an input unit 203, a display unit 204 display a washing course and an operation status of the washing machine 100, a first door 201 provided at the front upper part of the main body 301 to enter a small amount of laundry in a washing tub, and a second door 202 provided at the front lower end of the main body 301 to enter a large amount of laundry in a washing tub. The input unit 203 is provided at the center of the main body 301, includes a course and function button to select a washing course of each washing tub and a washing function, and enters user commands associated with washing courses and operations of the washing machine 100.

FIG. 2 is a cross-sectional view illustrating a configuration of a washing machine according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the washing machine 100 includes a plurality of washing tubs 302 and 303 to classify clothing according to the amount and type of the clothing and wash the classified clothing, and includes a first washing tub 302 to wash a small amount of laundry at an upper end and a second washing tub 303 to wash a large amount of laundry. In this case, the installation positions of the first and second washing tubs 302 and 303 may be changed to other positions. If necessary, the first and second washing tubs 302 and 303 may be composed of the washing tubs having the same capacity. The washing tubs may be classified into a large-capacity washing tub and a small-capacity washing tub according to characteristics of the washing machine 100 having several washing tubs. As described above, if a user desires to wash a small amount of laundry, the first washing tub 302 having the small capacity is driven only to prevent unnecessary power consumption. Meanwhile, a basic configuration of the first washing tub 302 is equal to that of the second washing tub 303. A first cylindrical drum 304 having a plurality of holes is provided in the first washing tub 302 and a second cylindrical drum 305 having a plurality of holes is provided in the second washing tub 303.

Two water-supply valves 306 a and 306 b and a water-supply hose 307 are provided at one side of the main body 301 of the washing machine. The water-supply hose 307 is divided into two parts, one of the two parts is connected to the first washing tub 302 through the water-supply valve 306 a, and the other part is connected to the second washing tub 303 through the water-supply valve 306 b, such that the first water-supply valve 306 a or the second water-supply valve 306 b may be selectively opened by a user command from the input unit 203, or the first and second water-supply valves 306 a and 306 b may be automatically opened to provide the first and second washing tubs 302 and 303 with water.

The first motor 310 a used as a driver rotating a first rotation shaft connected to the first drum 304 to perform washing, rinsing, and dehydration processes is installed at the exterior of the rear part of the first washing tub 302, and the second motor 310 b used as a driver for rotating a second rotation shaft connected to the second drum 305 is installed at the exterior of the rear part of the second washing tub 303.

The first motor 310 a is connected to a rotation wheel 311 a, connected to the first drum 304 by a shaft, through a belt. Likewise, the second motor 310 b is connected to a rotation wheel 311 b, connected to the second drum 305 by a shaft, through a belt.

Meanwhile, a drainage pipe 308 a draining dirty water is provided at one side of the first washing tub 302 and a drainage pipe 308 b is provided at one side of the second washing tub 303. The first and second drainage pipes 308 a and 308 b connected to each other at a lower part of the washing machine 100 have one outlet 309.

Although the washing machine 100 has exemplarily divided the first washing tub 302 and the second washing tub 303 in a vertical direction, the scope of an exemplary embodiment of the present invention is not limited thereto. The same purpose and effects of the embodiment of the present invention can be achieved even when the first and second washing tubs are installed in a horizontal direction.

FIG. 3 is a control block diagram illustrating a washing machine according to an exemplary embodiment.

Referring to FIG. 3, the washing machine 100 includes an input unit 203 entering a user's operation command including a dehydration process setup command, a controller 400 controlling overall operations (e.g., washing, rinsing, and dehydration processes) of the washing machine 100, a motor driver 410 driving a first motor 310 a and a second motor 310 b according to a control signal of the controller 400, and a speed detector 420 transmitting rotation speed signals of the motors 310 a and 310 b corresponding to rotation speeds of the drums 304 and 305 inside of the washing tubs 302 and 303 to the controller 400.

The input unit 203 may allow a user to select a washing course and a washing function for individual washing tubs 302 and 303, and may allow each washing tub 302 or 303 to enter a dehydration process according to a user's command.

The controller 400 adjusts an unbalanced position to reduce vibration generated by a dehydration operation of the washing machine 100. In more detail, the controller 400 determines whether a dehydration process is performed in the first washing tub 302 and the second washing tub 303. In still more detail, if a dehydration process is simultaneously performed in both of the washing tubs 302 and 303, the controller 400 detects an unbalanced position of each of the washing tubs 302 and 303, adjusts a dehydration rotation speed in the first or second washing tub 302 or 303, and thus controls a difference in unbalanced phase between the first tub 302 and the second tub 303 to be equal to or higher than a reference angle.

When the dehydration process is operating in only one of the first washing tub 302 and the second washing tub 303 of the washing machine 100, the controller 400 prevents the other washing tub from entering the dehydration process, resulting in reduced vibration.

When the dehydration process is operating in only one of the first washing tub 302 and the second washing tub 303 of the washing machine 100, and the other washing tub 302 or 303 enters the dehydration process, a dehydration rotation direction of the first or second washing tub 302 or 303 is changed to an opposite dehydration rotation direction, and the dehydration process having the opposite dehydration rotation direction is performed in the first or second washing tub 302 or 303, thereby reducing vibration of the washing machine 100. Meanwhile, if the dehydration rotation directions of two washing tubs 302 and 303 are opposite to each other, unbalanced rotation directions of the washing tubs 302 and 303 are also opposite to each other, so that vibration of the washing machine 100 may be reduced as compared to the case in which the washing tubs 302 and 303 have the same dehydration rotation direction.

The motor driver 410 outputs a drive signal, such as a PWM signal, to the first motor 310 a and the second motor 310 b upon receiving a control signal from the controller 400, thereby adjusting speeds of the first and second motors 310 a and 310 b.

The speed detector 420 may be implemented by a hall sensor or an encoder, and transmits a motor speed signal corresponding to the number of rotations of each of the first motor 310 a and the second motor 310 b to the controller 400.

FIGS. 4A and 4B illustrate unbalanced positions caused by laundry contained in the washing machine 100. FIG. 4C is a graph illustrating a variation of dehydration speed under an unbalanced status of the washing machine 100.

Referring to FIG. 4A, if the position of an unbalance 500 generated when the drums 304 and 305 of the washing tubs 302 and 303 rotate in a dehydration process moves upward, a rotation speed of each of the drums 304 and 305 is reduced. Referring to FIG. 4B, if the unbalanced position 500 moves downward, a rotation speed of each drum 304 or 305 is accelerated. The speed variation is generated when gravity is applied to the unbalance, and the speed variation of the drum 304 or 305 is denoted by a graph shown in FIG. 4C. In this case, a difference (p) between a maximum value and a minimum value in the graph is a variable according to the weight of unbalance 500 caused by laundry, and this difference (p) may have a tendency to be proportional to the unbalance 500.

Herein, considering the gravity effect caused by mass of the unbalance 500, it can be recognized that the position of the unbalance 500 may be located at the lowest point A of each drum 304 or 305 at a specific time when the drum 304 or 305 reaches the highest speed. In contrast, it can be recognized that the position of the unbalance 500 may be located at the highest point B of each drum 304 or 305 at a specific time when the drum 304 or 305 reaches the lowest speed.

Meanwhile, when the unbalance 500 arrives at the lowest point A and the highest point B of the drum 304 or 305, the rotation acceleration of the drum 304 or 305 becomes zero (i.e., a slope of 0 on a time-speed graph). In more detail, when the rotation acceleration becomes zero while the rotation speed of the first or second drum 304 or 305 increases and then decreases, the unbalance 500 is located at the highest point of the first or second drum 304 or 305. In contrast, when the rotation acceleration becomes zero while the rotation speed of the first or second drum 304 or 305 decreases and then increases, the unbalance 500 is located at the lowest point of the first or second drum 304 or 305.

FIGS. 5A and 5B are conceptual diagrams illustrating positions of unbalance occurring in a dehydration rotation operation of a washing machine 100 having a plurality of washing tubs according to an exemplary embodiment.

Referring to FIG. 5A, when the unbalance 510 of the first washing tub 302 is located at the right side, if the unbalance 520 of the second washing tub 303 is also located at the right side, a centrifugal force caused by a dehydration rotation of the first and second washing tubs 302 and 303 is equal to the resultant force (F=F′+F″), resulting in the occurrence of large variation. In other words, if positions of the unbalances 510 and 520 of two washing tubs 302 and 303 have the same phase, two forces F and F″ generating vibration by the dehydration rotation are summed up (F=F′+F″), so that total vibration of the washing machine 100 increases.

Referring to FIG. 5B, when the unbalance 510 of the first washing tub 302 is located at the left side, if the unbalance 520 of the second washing tub 303 is located at the opposite phase of the unbalance 510 of the first washing tub 302, a centrifugal force caused by rotation of each washing tub 302 or 303 is compensated (F=F″−F′), resulting in reduction of vibration.

In this case, according to one aspect of the present invention, the controller 400 controls the unbalanced positions of the first and second washing tubs 302 and 303 to have opposite phases (180 degrees) therebetween, and therefore the washing machine 100's vibration caused by the dehydration rotation can be reduced.

FIG. 6A is a flow chart illustrating a method of reducing vibration in a dehydration process of a washing machine according to an exemplary embodiment of the present invention.

Referring to FIG. 6A, if a control operation for reducing vibration of the washing machine 100 begins, the controller 400 determines whether a dehydration process is operating in the first washing tub 302 and the second washing tub 303 at operation S10.

The controller 400 determines whether the dehydration process is simultaneously operating in two washing tubs 302 and 303. If the dehydration process is simultaneously operating in the washing tubs 302 and 303 at operation S11, dehydration rotation directions of the first and second washing tubs 302 and 303 are opposite to each other at operation S13. In other words, if the first and second washing tubs 302 and 303 have the same dehydration rotation directions, any one of the dehydration rotation directions of the first and second washing tubs 302 and 303 is changed to an opposite dehydration rotation direction, and then a dehydration process is performed in the opposite dehydration rotation direction. If the dehydration rotation directions of the first and second washing tubs 302 and 303 are opposite to each other, a conventional rotation direction is maintained, such that a dehydration process is performed in the conventional dehydration rotation direction. In this case, a dehydration rotation direction of one washing tub 302 or 303, having a relatively low dehydration rotation speed, between the first washing tub 302 and the second washing tub 303 can be changed at operations S11 and S13.

Next, the controller 400 performs an unbalanced position control at operation S16. In this unbalanced position control, the controller 400 confirms unbalanced positions of the first and second washing tubs 302 and 303, and reduces vibration of each washing tub by adjusting the confirmed unbalanced positions. A detailed description thereof will be described with reference to FIG. 7.

In the meantime, when a dehydration process is operating in only one (i.e., hereinafter referred to as a first washing tub) of the washing tubs 302 and 303 at operation S12, the controller 400 determines whether the other washing tub (i.e., hereinafter referred to as a second washing tub) performing no dehydration process reaches a dehydration process at operation S14.

If the second washing tub 302 or 303 performing no dehydration process reaches the dehydration process, the controller 400 performs a dehydration rotation operation in another dehydration rotation direction different from that of the first washing tub 302 or 303 which performs the dehydration operation earlier than the second washing tub 302 or 303, at operation S15.

In this case, the second washing tub 302 or 303 performs a dehydration process in a dehydration rotation direction opposite to that of the first washing tub 302 or 303 which performs the dehydration process earlier than the second washing tub 302 or 303, resulting in reduction of vibration of the washing machine 100.

FIG. 6B is a flow chart illustrating a method of reducing vibration in a dehydration process of a washing machine according to another exemplary embodiment of the present invention.

The method of FIG. 6B is different from that of FIG. 6A, because the method of FIG. 6B, when a dehydration process is operating in only one of the first and second washing tubs 302 and 303 of the washing machine 100, prevents the other washing tub 302 or 303 performing no dehydration process from entering the dehydration process.

Referring to FIG. 6B, if the vibration reduction control operation of the washing machine 100 begins, the controller 400 determines whether the dehydration process is operating in the first and second washing tubs 302 and 303 at operation S20.

Next, the controller 400 determines whether the dehydration process is simultaneously operating in two washing tubs 302 and 303 at operation S21. If the dehydration process is simultaneously operating in two washing tubs 302 and 303, dehydration rotation directions of the first and second washing tubs 302 and 303 are opposite to each other at operation S23.

Next, the controller 400 confirms unbalanced positions of the first and second washing tubs 302 and 303. The controller 400 performs an unbalanced position control operation that reduces vibration of the washing machine by adjusting the confirmed unbalanced positions at operation S26.

Meanwhile, when a dehydration process is operating in one washing tub 302 or 303 at operation S22, the controller 400 determines whether the other washing tub 302 or 303 performing no dehydration process enters a dehydration process at operation S24.

If it is determined that the washing tub 302 or 303 performing no dehydration process reaches the dehydration process, the controller 400 prevents the washing tub 302 or 303 reaching the dehydration process from entering the dehydration process at operation S25.

The controller 400 determines whether the washing tub 302 or 303 performing the dehydration operation finishes the dehydration operation at operation S27. If it is determined that the dehydration process is completed at operation S27, the controller 400 performs a dehydration operation of the washing tub 302 or 303 reaching the dehydration process at operation S28.

FIG. 6C is a flow chart illustrating a method of reducing vibration in a dehydration process of a washing machine according to another exemplary embodiment of the present invention.

The method of FIG. 6C is different from that of FIG. 6A, because the method of FIG. 6C does not control dehydration rotation directions of the first and second washing tubs 302 and 303 to be opposite to each other, when a dehydration process is simultaneously operating in two washing tubs 302 and 303.

Referring to FIG. 6C, if the vibration reduction control operation of the washing machine 100 begins, the controller 400 determines whether a dehydration process is operating in the first and second washing tubs 302 and 303 at operation S30.

Next, the controller 400 determines whether the dehydration process is simultaneously operating in two washing tubs 302 and 303 at operation S31. If the dehydration process is simultaneously operating in two washing tubs 302 and 303 at operation S31, the controller 400 confirms unbalanced positions of the first and second washing tubs 302 and 303, and performs an unbalanced position control reducing vibration of the washing machine by adjusting the confirmed unbalanced positions at operation S35.

Meanwhile, when the dehydration process is operating in only one washing tub 302 or 303 at operation S32, the controller 400 determines whether another washing tub 302 or 303 performing no dehydration process enters the dehydration process at operation S33.

If the washing tub 302 or 303 performing no dehydration process enters the dehydration process at operation S33, the controller 400 performs a dehydration rotation operation in another dehydration rotation direction different from that of the other washing tub 302 or 303 which performs the dehydration operation earlier than the above washing tub, at operation S34.

Next, the controller 400 performs an unbalanced position control operation reducing vibration of the washing machine 100 by adjusting unbalanced positions.

FIG. 6D is a flow chart illustrating a method of reducing vibration in a dehydration process of a washing machine according to another exemplary embodiment of the present invention.

The method of FIG. 6D is different from that of FIG. 6B, because the method of FIG. 6D does not control dehydration rotation directions of the first and second washing tubs 302 and 303 to be opposite to each other when a dehydration process is simultaneously operating in two washing tubs 302 and 303.

Referring to FIG. 6D, if the vibration reduction control operation of the washing machine 100 begins, the controller 400 determines whether the dehydration process is operating in the first and second washing tubs 302 and 303 at operation S40.

Next, the controller 400 determines whether the dehydration process is simultaneously operating in two washing tubs 302 and 303 at operation S41. If it is determined that the dehydration process is simultaneously operating in two washing tubs 302 and 303 at operation S41, the controller 400 confirms unbalanced positions of the first and second washing tubs 302 and 303, and performs an unbalanced position control operation to reduce vibration of the washing machine by adjusting the confirmed unbalanced positions at operation S45.

If the dehydration process is operating in only one washing tub 302 or 303 at operation S42, the controller 400 determines whether the other washing tub 302 or 303 performing no dehydration process reaches the dehydration process at operation S43.

If the washing tub 302 or 303 performing no dehydration process reaches the dehydration process, the controller 400 prevents the washing tub 302 or 303 reaching the dehydration process from entering the dehydration process at operation S44.

The controller 400 determines whether the dehydration operation is completed in the washing tub 302 or 303 performing the conventional dehydration operation at operation S46. If it is determined that the dehydration operation is completed at operation S46, the controller 400 performs the dehydration operation of the washing tub 302 or 303 having reached the dehydration process at operation S47.

FIG. 7 is a flow chart illustrating a method of controlling an unbalanced position of a washing machine 100 according to an exemplary embodiment of the present invention.

Referring to FIG. 7, when a dehydration process is operating in the first and second drums 304 and 305 rotatably installed in the first and second washing tubs 302 and 303, the controller 400 determines whether a rotation speed of each of the first and second drums 304 and 305 reaches a steady state at operation S51. In this case, the rotation speeds of the first and second drums 304 and 305 are respectively equal to those of the first motor 310 a and the second motor 310 b at operation S50.

Next, if the rotation speeds of the first and second drums 304 and 305 reach a steady state at operation S51, the controller 400 detects unbalanced positions of the drums 304 and 305 at operation S52. In more detail, at operations S51 and S52, the controller 400 receives information about rotation speeds of the first and second drums 304 and 305 from the speed detector 420, checks that the speed of each drum 304 or 305 is changed at intervals of a predetermined time, recognizes a time point, where the speed of the drum 304 or 305 increases and then decreases, as the lowest unbalanced position A of the washing tub, and recognizes another time point, where the speed of the drum 304 or 305 decreases and then increases, as the highest unbalanced position B of the washing tub.

The controller 400 controls a dehydration rotation speed (S52) when the unbalanced position is detected. In other words, the controller 400 adjusts the speed of any one or both of the first drum 304 and the second drum 305, to control an unbalanced position difference angle (i.e., a phase difference) between the first drum 304 and the second drum 305 to reach a reference angle. Herein, the reference angle may be optionally set by a designer, and may be ideally set to 180°. For example, when the unbalanced position of the first washing tub 302 is located at the lowest point of the first washing tub 302 and the unbalanced position of the second washing tub 303 is located at the highest point of the second washing tub 303, an unbalanced position difference angle between the first washing tub 302 and the second washing tub 303 is 180° at operation S53.

In the meantime, the unbalance position difference angle represents a phase difference angle between unbalanced positions of individual washing tubs 302 and 303. The unbalanced position control method of FIG. 7 prevents a centrifugal force F caused by a dehydration rotation of two drums 304 and 305 from increasing in response to the increasing position difference angle.

As is apparent from the above description, the washing machine and a method of controlling the same according to embodiments of the present invention can reduce vibration of the washing machine by adjusting unbalanced positions of two washing tubs in a dehydration process of the washing machine having the two washing tubs.

In accordance with another aspect of the present invention, two dehydration rotation directions are adjusted to be opposite to each other in a dehydration process of a washing machine having two washing tubs. In addition, when one of the two washing tubs is in a dehydration process, the control method prevents the other washing tub from entering a dehydration process, thus reducing vibration of the washing machine.

Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents. 

1. A method of controlling a washing machine having a first washing tub and a second washing tub, the method comprising: determining whether a dehydration operation is performed in the first and second washing tubs; and reducing vibration of the washing machine comprising adjusting the dehydration operation of the first or second washing tub.
 2. The method according to claim 1, wherein the determining whether the dehydration operation is performed in the first and second washing tubs includes: determining, when one of the first and second washing tubs is in the dehydration process, whether the other of the first and second washing tubs performing no dehydration operation begins a dehydration operation.
 3. The method according to claim 2, further comprising: controlling, if the other of the first and second washing tubs having no dehydration operation beings the dehydration operation, the dehydration operation of the other of the first and second washing tubs comprising performing a dehydration rotation in a direction opposite to a dehydration rotation direction of the one of the first and second washing tubs in which the dehydration operation is performed.
 4. The method according to claim 2, further comprising: controlling, if the other of the first and second washing tubs having no dehydration operation begins the dehydration operation, a dehydration operation of the other of the first and second washing tubs to prevent the other of the first and second washing tubs from entering the dehydration operation until the washing tub performing the dehydration operation stops the dehydration operation.
 5. The method according to claim 1, wherein the determining whether the dehydration process is performed in the first and second washing tubs includes: determining whether the first and second washing tubs simultaneously begin the dehydration operation.
 6. The method according to claim 5, further comprising: setting, if the first and second washing tubs simultaneously begin the dehydration operation, different dehydration rotation directions, so that the dehydration operations of the first and second washing tubs are performed in different directions.
 7. The method according to claim 5, further comprising: adjusting, if the first and second washing tubs simultaneously begin the dehydration operation, a dehydration operation of the washing tub in such a manner that the dehydration operation is performed only in one of the first and second washing tubs.
 8. The method according to claim 7, further comprising: adjusting a dehydration operation of the washing tub having no dehydration operation in such a manner that the washing tub having no dehydrating operation begins the dehydration operation when the dehydration operation of the washing tub having the dehydration operation is completed.
 9. The method according to claim 1, wherein the determining whether the dehydration process is performed in the first and second washing tubs includes: determining whether the first and second washing tubs simultaneously perform the dehydration operation.
 10. The method according to claim 9, further comprising: checking an unbalanced position of each of the first and second washing tubs when the first and second washing tubs simultaneously perform the dehydration operation.
 11. The method according to claim 10, wherein: a first drum is rotatably installed in the first washing tub, and a second drum is rotatably installed in the second washing tub, and the checking of the unbalanced position comprises detecting a rotation speed of the first or second drum.
 12. The method according to claim 11, wherein the checking of the unbalanced position by detecting the rotation speed of the first or second drum includes: checking a position at which a rotational acceleration of the first or second drum becomes zero.
 13. The method according to claim 12, wherein the checking of the unbalanced position by detecting the rotation speed of the first or second drum further includes: determining that the unbalanced position is at a highest point of the first or second drum at a time at which the rotational acceleration becomes zero in response to an increasing and decreasing of the rotation speed of the first or second drum.
 14. The method according to claim 13, wherein the checking of the unbalanced position by detecting the rotation speed of the first or second drum further includes: determining that the unbalanced position is at a lowest point of the first or second drum at a time at which the rotation acceleration becomes zero in response to the increasing and decreasing of the rotation speed of the first or second drum.
 15. The method according to claim 10, further comprising: adjusting, if the unbalanced position of the first or second washing tub is checked, an unbalanced position of the first or second washing tub, and reducing the vibration of the washing machine.
 16. The method according to claim 15, wherein the adjusting of the unbalanced position of the first or second washing tub includes: controlling a difference between a first position angle of an unbalance of the first washing tub and a second position angle of an unbalance of the second washing tub to be equal to or larger than a reference angle.
 17. The method according to claim 15, wherein the adjusting of the unbalanced position of the first or second washing tub includes: adjusting the unbalanced position comprising adjusting a dehydration rotation speed of the first or second washing tub.
 18. The method according to claim 9, further comprising: setting, if the dehydration operation is simultaneously performed in the first and second washing tubs, different dehydration rotation directions to the first and second washing tubs, and adjusting the dehydration operations of each of the washing tubs.
 19. The method according to claim 18, further comprising: checking dehydration rotation speeds of the first and second washing tubs; and changing the rotation direction of the washing tub having a relatively slow dehydration rotation speed from among the first and second washing tubs to another rotation direction, and adjusting the dehydration operation of the washing tub in the changed rotation direction.
 20. A washing machine comprising: a plurality of washing tubs; and a controller which checks whether a dehydration operation is performed in each of the washing tubs, adjusts the dehydration operation of each of the washing tubs when the dehydration operation is performed in each of the washing tubs, and reduces a vibration of the washing machine.
 21. The washing machine according to claim 20, further comprising a first drum and a second drum wherein: the plurality of washing tubs include a first washing tub in which the first drum is rotatably installed and a second washing tub in which the second drum is rotatably installed, and the controller reduces vibration of the washing machine by adjusting rotation operations of the first and second drums.
 22. The washing machine according to claim 21, further comprising: a speed detector to detect a speed of the first or second drum.
 23. The washing machine according to claim 22, wherein the controller checks an unbalanced position of the first or second washing tub according to a speed of the first or second drum.
 24. The washing machine according to claim 23, wherein the controller reduces vibration of the washing machine by adjusting the unbalanced position of the first or second washing tub.
 25. The washing machine according to claim 24, wherein the controller adjusts a difference in the unbalanced position between the first washing tub and the second washing tub to be equal to or larger than a reference angle.
 26. The washing machine according to claim 21, wherein the controller reduces the vibration of the washing machine by controlling the first and second drums to have different dehydration rotation directions opposite to each other. 